SSB Whip antenna blind spot?

[kcj]

Preface this by I am NEW to the ssb world, and most of what I know I have absorbed from this site. Many thanks to all!

In the central exumas listening to Chris Parker on 4 MHz. I hear a call from a nearby anchorage and Chris hears it loud and clear. I call shortly thereafter and Chris cannot hear me, but someone (I believe) to the south of me hears me clearly and relays for me. Call is completed via relay.

Other bkgd, I have a new to me cat with a whip antenna mounted next to the aluminum solar panel structure. The solar panel structure is about 1/3 the height of the whip. I have done radio checks on 8mhz with Chris and they have worked fine. Have an icom 802 and AT400 tuner. Whip is installed two feet or less from tuner. DSC tests have been successful, but only at certain times of day--I assumed because of MHz propagation issues.

Query---what is causing this tx anomaly? can my solar panel structure be blocking my ssb tx signal in certain directions (the structure was between the antenna and Florida...)?

Thanks in advance!

[a64pilot]

There are all kinds of radio propagation issues, many due to the atmosphere, and this is constantly changing of course. To answer your question, yes there can be blind spots from metal blanking out the signal.

But even if you have the perfect installation, you will have issues transmitting, at times you will come in strong, other times you won't.
I'm not a Ham, but have used Military radios quite a bit, but I have a feeling if you take a Ham to lunch, and ask them this, first response will be a smile, as it will be sort of like that epiphany I had after buying a sailboat, you know the one when you realize that the wind is almost never right for where you want to go?

[transmitterdan]

Tell us about how the AT140 tuner "ground" is connected to the sea? Pictures are helpful.

[SoonerSailor]

A 23 foot whip antenna is not going to be the most efficient radiator at the relatively low frequency of 4 MHz. Your RF ground will be very important when using a short for frequency antenna like this, as transmitterdan is getting at. That might be one part of the problem.

Other factors will be time of day and how close you or the other station are to Chris. And of course the radiation pattern of your antenna vs that of the other station. What the take-off angle is, what kind of azimuthal lobes your antenna has on that band, and many other possible influences.

Chip


Sent from my iPhone using Cruisers Sailing Forum

[kcj]

The ground is 1.5" copper strap from tuner in port engine compartment up thru bilge on port side. It also appear to tie into some grounding plates.. I do not know how to check the ground beyond that.

Am going to try a rope antenna on st loan to see if it's the antenna length and am going to monitor battery voltage as well, we were close to 12v this am when trying to transmit (reasonablely unsuccessfully...). But that's a different issue I'm trying to resolve in paradise...

Cheers, John

[transmitterdan]

The length of the wire from the tuner to the antenna is not critical. The length of the ground strap is important. It sounds as if the installer positioned the tuner close to the antenna and far from the grounding plate. If so it might work better by relocating the tuner closer to the grounding plate and using a longer antenna feed wire to connect the tuner to the antenna.

Voltage at the radio is critically important. What is the length and size of the wiring from the battery to the radio power unit?

[roverhi]

The tuner should be as close to the antenna as possible. The antenna starts from the wire at the tuner, not where the wire from the antenna tuner attachs to the stay or whatever you calling an antenna. The grounding run for the tuner counterpoise shouldn't be more than 15' if going to something in contact with the water.

The ground does not need to attach to the water. Copper strapping above the water line that runs from bow to stern underneath the deck on each side has worked fine for me. Would probably be better if it was connected to metal bits like tanks pulpits and stanchions along the way. There seems to be a bit of magic involved in establishing a good antenna ground counterpoise as some have gotten by running a copper strap to a convenient through hull.

Might want to look at your whip antenna. My understanding is that these are designed to work with specific frequencies. If you are trying to get out on a frequency they aren't designed for the signal will suffer.

This is a good primer on boat HF SSB radio http://www.farallon.us/webstore/Pcup%20SSB.pdf:

[Skuzzlebutt]

roverhi, This does not appear to be a valid URL, could you please check?
Thanks,

[SoonerSailor]

The ubiquitous 23' whip antenna for SSB will "work" on any frequency when properly matched to the transmitter's output impedance through a "tuner". It would be considered a resonant antenna at a frequency of about 20 MHz, but above or below that will require a way to match it to the transmitter. The lower your frequency, the harder it is for the tuner to make a match, the less is the radiation efficiency of the antenna, and for RF electrical reasons the more important a low impedance connection to an RF ground. Lots of cruisers do fine with such an antenna, even if they are giving up some radiated signal strength.

A better antenna is one matched to the specific frequency of interest, and the vertical dipole as described by Bill Trayfors is one of the very best for a boat. One for the 20 meter band is quite doable on the typical cruising boat, and that is also one of the best bands for long distance HF communications under varying circumstances.

Chip

[waterman46]

You say you have done successful radio checks with Chris Parker, but you didn't mention the time of day and frequency. Assuming your radio check was also on 4MHz, I think you are correct in thinking its possible your signal was being blocked by some structure on your boat in its current heading. I say this because at 4MHz there should be very little propagation difference from a "nearby" anchorage and your location, and your antenna is not real high.


Next time you have a similar issue, fire up and turn the boat 90 degrees and see what happens!

[snarron]

Correct address:
http://www.farallon.us/webstore/Pcup%20SSB.pdf

if this doesn't work, delete </Pcup%20SSB.pdf> and choose the primer in left side menu. ;-)

[transmitterdan]

Originally Posted by roverhi

The tuner should be as close to the antenna as possible.

This is not right in my experience. A little extra antenna length doesn't hurt anything. But 15' of ground strap is nearly useless at HF frequencies. The ground needs to be low impedance (i.e. short) and connecting it to salt water is the best ground you can get. If there is no short way to get to water then make a grid of copper but keep the strap from tuner to mat short.

Originally Posted by roverhi

The antenna starts from the wire at the tuner, not where the wire from the antenna tuner attachs to the stay or whatever you calling an antenna.

That's correct but having a little extra antenna length usually isn't harmful especially on a short whip.

There is no magic in using a nearby through hull for the tuner ground. Seawater makes a very good counter poise.

[Seafari]

this is a great read for anyone interested in SSB http://www.sgcworld.com/Publications...fguidebook.pdf

[ka4wja]

kcj,
As others have written, there are intricacies and variables in radiowave propagation, but also in antenna radiation patterns and efficiencies...as well as the antenna ground system....

I hope you don't mind my comments here, and I won't boast too much but I've studied radiowave propagation and antenna system design for the past 45 years, and have spent a good deal of time during the past 35 - 40 years teaching these very subjects.....
So, perhaps I can give you some "straight scoop"...

~~~~~

Please take note that there are still many Icom M-802's out there that have never had the factory "clipping mod" done, and as such suffer from this defect....
As well as many M-802's that do not have their DSP-based "speech compression" turned on....
Either of these issues could be the proximate cause of your troubles....

Do you know the specifics of your radio???

Please have a look at these pages for more details...
Icom M-802 "Clipping Issue" - Revisited....

--- Remember that this "clipping issue" effects ONLY Voice SSB communications with the M-802, not DSC, CW, FSK, nor any data modes using a PACTOR modem, only Voice SSB...so those that "think" their radio works fine (but maybe haven't ever used it on Voice SSB, or maybe had difficulty making Voice SSB contacts but assumed their radio is working and that "SSB is full of static, etc.), should investigate this BEFORE they leave port....verify their M-802's serial number and test it on-the-air with other vessels and shore stations (using SSB Voice)...

Everyone should verify that their radios are working properly and optimally, BEFORE leaving port on a long passage ....and with many early versions of the M-802 still being sold/installed ("new old stock"), it is very important for everyone to verify the M-802's s/n, and if it's below 0108261, they should have an Icom Service Center do the "clipping fix modification" (it is FREE)....but everyone, no matter what their M-802's serial number, should verify that their radio is working correctly...

IC-M802 Compression

--- As for the "Speech Compressor", since the M-802 was 1.5db shy of meeting the commercial specs at 150 watts output (but does meet the spec at 100-125 watts), Icom USA decided to ship most of the M-802's with its very nice and clean DSP-based Speech Compressor turned off....and hence many M-802's sound a bit "weak" on-the-air, again on Voice SSB communications only....(this does NOT have any effect on DSC, CW, FSK, nor any PACTOR modes, only Voice SSB...)
Turning the Speech Compressor ON (done via software by an Icom certified radio tech / installer) takes just a few seconds and doesn't produce any harmful transmit effects, but rather seriously increases the radio's average output power ("talk power") and makes the M-802 a "loud-and-clear" radio on-the-air!!
I highly recommend doing this....

~~~~~~~~~~~~


Okay, now on with the radiowave propagation and antenna system / pattern answers!
1) But, before I delve into the details, if you have decent internet access, please have a look at these videos....

Maritime HF Comms
https://www.youtube.com/playlist?lis...ZDo_Jk3NB_Bt1y


Offshore Weather
https://www.youtube.com/playlist?lis...zdjTJjHlChruyY


HF-DSC Comms
https://www.youtube.com/playlist?lis...ga2zYuPozhUXZX


Icom M-802 Instruction Videos
https://www.youtube.com/playlist?lis...rC-8QKVyMb4tVr


As well as be sure to read the "sticky" that is at the top of the "Marine Electronics" page...
http://www.cruisersforum.com/forums/...tc-133496.html


And, have a look here:
HF Radio Freqs, summertime Atlantic crossing, offshore Net..

Tips for using an HF-SSB Radio (mostly for newcomers)


And, these have some detailed explanations of the various videos...
http://www.cruisersforum.com/forums/...os-141406.html

http://www.cruisersforum.com/forums/...ll-114734.html



2) Secondly, here is some "cruising boat" specific info:

a) Because vertical antennas have nulls overhead, they tend to be VERY poor antennas for "regional" / short-range HF comms (from 100 miles to 400 miles), which are supported by Near Vertical Incidence Skywave (NVIS) propagation.
{although "groundwave" comms over sea water on the lower HF bands, can be quite good with vertical antennas....allowing good signals out 100 miles or more...}

b) So the common recommendation of using the HIGHEST frequency that will support the communications, at that time-of-day and communications distance (where signals are typically stronger, D-layer absorption is lower, and fading is less) is even more important for covering these "regional" distances (100 - 500 miles), with our vertical antennas...
{note that those with horizontal antennas (such as hams on shore, etc.), have a very distinct, significant advantage in using NVIS propagation to cover regional distances out to 500 miles or so, on freqs from 2mhz thru 10mhz (but typically 3.5 - 7/8mhz daytime....and 1.8/2mhz thru 5mhz nighttime)...}

c) Don't forget the main goal here is S/N (signal to noise ratio), so reducing noise and improving the signal strength (by using a higher frequency, eliminating on-board RFI, etc.), are fairly important when dealing with using vertical antennas for regional HF comms on-board.

d) Understand that these radiowave propagation and antenna pattern facts here, have been ignored by many (most) in the sailing/cruising community for decades....
And, in my 45 years of sailing/cruising (and radio), I'm still at a loss to understand why!
But, regardless.....if you learn from these facts, you will be well ahead of 90% of your fellow cruisers (and surprisingly better informed than most hams as well!)



3) How about some specifics....

Originally Posted by kcj

Preface this by I am NEW to the ssb world, and most of what I know I have absorbed from this site. Many thanks to all!
Watch the videos, and read the reference material....
(and don't be too quick in looking for an answer to some anomaly.....many times the "quick internet answer" is false...)


In the central exumas listening to Chris Parker on 4 MHz. I hear a call from a nearby anchorage and Chris hears it loud and clear. I call shortly thereafter and Chris cannot hear me, but someone (I believe) to the south of me hears me clearly and relays for me. Call is completed via relay.
See all details above...



Other bkgd, I have a new to me cat
Without knowing your M-802's serial number, nor its history.....we do not know the status of your M-802, as in regards to the "clipping mod" nor the "speech compression"
Please verify your M-802's serial number....if it is below 0108261, then you may very well have the old clipping problem (which can be easily repaired by Icom, for FREE), and this could be a significant part of your problem!
Also, please read over the above referenced info, that should allow you to verify whether your M-802 has its internal DSP-based "speech compression" turned on or not...(I highly suspect not!)
(see details above)


Other bkgd, I have a new to me cat with a whip antenna mounted next to the aluminum solar panel structure. The solar panel structure is about 1/3 the height of the whip.
Typically structure that is not parallel to the antenna has little effect....and the set-up you describe should have no practical effect....
(although, please do take note that the relatively short 23' whip, vs. a 45' backstay antenna, will always produce a weaker signal on the lower HF bands, especially 4mhz)

I have done radio checks on 8mhz with Chris and they have worked fine. Have an icom 802 and AT400 tuner. Whip is installed two feet or less from tuner. DSC tests have been successful, but only at certain times of day--I assumed because of MHz propagation issues.
Yes, but their not really "issues" any more than it being light out during the day and dark out at night are "issues".....
Rather, radiowave propagation is just another aspect of life / physics....it is well understood and there are dozens / 100's of books on the subject....
But, not to worry.....if you just watch the videos and read over the above referenced materials, you know more about it than 90% of your fellow cruisers, and you'll be fine!


Query---what is causing this tx anomaly?
See all details above...


can my solar panel structure be blocking my ssb tx signal in certain directions (the structure was between the antenna and Florida...)?
No....
(well anything is possible to some degree....but it's a 1000 to 1 shot at best, that this anything to do with your problem....and even if it did make it to that 1000:1 shot, the difference would be slight.)
Thanks in advance!

There is actually quite a bit more to write and explain....
But, until I know some more (your M-802's serial number, whether it's had the "clipping mod" done, whether it's DSP-based "speech compression" is on, etc.), I don't want to get ahead of myself.....
(nor do I want to overwhelm you!)



BTW, you may note that I barely mentioned (never?) the "grounding system"....
This is not because it isn't important (it IS), but because it is such a controversial subject, that I wanted to hit upon the horses first and then deal with the zebras!!!
(oh, and yes.....I do have a great deal of experience with vertical antenna grounds / rf grounds!)
And, transmitterdan gave you sound input regarding them....



I hope this helps..

Fair winds..

John